Dinamic of pathogenic protozoa and cyanobacteria in a reservoir used for water supply in southeastern Brazil

ABSTRACT

The current study monitored the water quality of a tropical reservoir (Vargem das Flores) used to supply potable water to seven cities in the metropolitan area of Belo Horizonte, Minas Gerais, southeast Brazil. The reservoir was monitored for four years: initially (from 2004 to 2007) for cyanobacterial cells and physicochemical parameters and, subsequently (in 2007 and 2008), for Cryptosporidium spp. oocysts and Giardia spp. cysts in four sampling stations. The concentrations of Escherichia coli were also measured in 2007 and 2008, wich allowed the characterization of each sampling point according to the National Environment Council (CONAMA) no. 274/2000. Results indicated concentrations of Cryptosporidium spp. and Giardia spp. (oo)cysts ranging from 0 to 0.8 (oo)cysts.L^-1, and higher concentrations of cyanobacteria cells, from 0.0 to 4.5 x 10⁵ cells.mL^-1, thus indicating potential risks to human health, if the water from the reservoir is not properly treated before consumption. The group of cyanobacteria was not found during the dry season, returning soon after destratification. The rainy season was characterized by a higher ocurrence of cyanobacteria and predominance of picoplanktonic species (Aphanocapsa spp.), over the Microcystis spp. previously found and presented the highest variations in dissolved oxygen, turbidity, total phosphorous, orthophosphate, ammonia, nitrite and nitrate. The change observed within the group of cyanobacteria (Aphanocapsa spp. over Microcystis spp.) may be indicative of changing characteristics in the water source. All the sampling points were classified as adequate for primary contact recreation, given the E. coli concentrations, according to the CONAMA Resolution no. 274/2000.

Keywords:
public water supply; water quality; Cryptosporidium oocysts; Giardia cysts; cyanobacteria; tropical reservoir; Escherichia coli; CONAMA no. 274/2000